1. Field of the Invention
The present invention relates to a sensor system with frequency modulated continuous wave FMCW radar and with a mechanism for correcting phase errors.
In sensor systems with FMCW radar, particularly microwave radar systems, a simultaneous distance and speed measurement is possible. These types of sensor systems have multiple application possibilities, such as in automotive or automation technology. In a sensor of this type, a frequency-modulable signal source (e.g. a microwave oscillator) is present, which emits a linearly frequency-modulated transmit signal via a transceiver (e.g. one or more antennae), for example. The signal, which is received after a delay of the transit time to a measurement subject and back, is separated from the transmit signal as a receive signal by a transceive separating filter and is forwarded to a mixer. In this mixer, the receive signal is demodulated with the transmit signal. A low-pass filtering preferably occurs subsequently, in order to eliminate undesirable frequency portions. In this type of sensor, the information about the distance between the transceiver and the measurement subject is proportional to the phase-angle deviation ( or respectively, the frequency) of the measuring signal. By virtue of this fact, in practice primarily errors of the phase of the signal have a limiting effect on the performance capability (range, measurement accuracy, sensitivity) of the system. For example, as such phase errors, stochastically distributed errors can arise which originate in a phase noise of the signal source. When measurement distances are great, such errors have disadvantageous effects. For example, systematic phase errors are brought about by a non-ideally linearly progressing frequency modulation of the signal source. Errors of this type frequently interfere considerably, even given measurement in the near environment.
2. Description of the Prior Art
In order to suppress these types of phase errors in the described sensors, an appreciable technical outlay is required. DE 27 10 841 A1 teaches an arrangement for measuring distance wherein a linearly frequency-modulated oscillator is used, and mechanisms are provided which correct deviations from the linearity of the modulation with the aid of a delay line and a control loop.